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    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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<body>
    <script>
        //1,2,3
        //异步变同步
        console.log(1);   
        // Promise 异步任务同步化
        // 许诺 Promise 包含一个耗时性的任务 
        const p = new Promise((resolve)=>{
            //执行
            setTimeout(function() {
            console.log(2);
            resolve();
        }, 3000)
        })
        p.then(()=>{
            console.log(3);
        })
        console.log(4);
    </script>
</body>
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